1. Field of the Technology
The present technology relates to an image forming apparatus.
2. Description of the Related Art
Image forming apparatuses such as a copying machine, a printing machine, a printer and a facsimile machine generally employs an electrophotographic method, an electrostatic recording method, and the like using toner. For example, in an electrophotographic image forming apparatus is used a photoreceptor drum on a surface of which a photosensitive layer containing a photoconductive substance is formed. In such an image forming apparatus is formed an image as follows: the surface of the photoreceptor drum is uniformly charged by giving electric charges to the surface of photoreceptor drum, an electrostatic latent image corresponding to image information is formed in various image forming processes, the electrostatic latent image is developed by use of toner supplied from a developing section to make a toner image, the resultant toner image is transferred to a recording material such as paper, directly or with assistance of an image carrier, and the toner image on the recording material is subjected to fixing process.
Currently-adopted fixing methods for fixing the unfixed toner image onto the recording material include: a heat fixing method that the unfixed toner image on the image carrier or recording material is heated; and a wet fixing method that fixer fluid having a toner-softening action is applied to a toner image on the image carrier or recording material.
The heat fixing method is such a method that a toner image on the image carrier such as an intermediate transfer belt, or on the recording material is heated into a fused state, and this fused toner image is fixed on the recording material by pressure. For example, an image forming apparatus has been proposed in which a toner image is transferred and fixed onto a recording material in a heated state by heating not only the toner image on the image carrier but also the recording material to which the toner image has not been transferred and fixed (for example, see Japanese Unexamined Patent Publication JP-A 2004-151626).
In this image forming apparatus, fixing force of the toner image onto the recording material is enhanced, but there is a problem that it is not possible to perform a heat fixing operation until a temperature of a heating section rises up to a temperature (which will be hereinafter referred to as “a predetermined temperature” unless particularly mentioned) necessary for fusing the toner, so that a standby time lasting until reach of the predetermined temperature, namely a warm-up time will be required and in particular, when the image forming apparatus is activated, the warm-up time is longer than usual. Further, even when the temperature of the heating section has reached the predetermined temperature, there is still a problem that a large amount of successive image formations results in delay of a heating operation conducted by the heating section, which is to be complied with the image formation, to therefore lead an insufficient heat fixing property of the toner image. The image forming apparatuses of the heat fixing method have the above-mentioned problems in common.
On the other hand, in the wet fixing method, fixer fluid having a toner-softening action is applied to the toner image on the image carrier or recording material to thereby soften the toner image so as to fix the softened toner image onto the recording material by pressure. An advantage of the wet fixing method is an extremely small power consumption compared to that in the heat fixing method. For this reason, an image forming apparatus of combined wet fixing method and heat fixing method has been proposed.
For example, there has been proposed a fixing apparatus in which a coating roller carrying on a surface thereof fixer fluid comes into contact with a toner image carried on an image carrier or recording material so that the fixer fluid is applied selectively to only a toner attached portion of the toner image, and the toner and the fixer fluid are heated (for example, see Japanese Unexamined Patent Publications JP-A 2004-109747). That is to say, this fixing apparatus employs a method in which heating is conducted by a heating section after the fixer fluid is applied to the toner image on the image carrier or recording material. By thus heating the toner image to which the fixer fluid has been applied, softening of the toner is promoted so that a transferring-fixing property of the toner image onto the recording material is enhanced. Furthermore, evaporation of excess liquid contained in the fixer fluid is promoted, so that an amount of the fixer fluid attached to the recording material is minimized, with the result that there exists an advantage that wrinkles, curls and the like defects are prevented from being generated in the recording material.
Further, JP-A 2004-109747 discloses the following constitution. That is, in a case where the toner image is carried on the image carrier, an intermediate transfer belt serving as the image carrier is treated with water-shedding processes such as fluorine treatment. Accordingly, in a case where the fixer fluid is applied to an unfixed toner image on the intermediate transfer belt, the fixer fluid gathers only on a toner portion (an image portion) while the fixer fluid does not stagnate on a portion where the toner does not exist (a non-image portion).
However, in the image forming apparatus described in JP-A 2004-109747, the fixer fluid is used indispensably for softening the toner image and as a result, a usage of the fixer fluid is large. This poses a problem that it is necessary to replenish a large amount of the fixer fluid frequently. This is especially prominent in a high-speed machine which outputs a large number of sheets per hour. The frequent replenishment of the fixer fluid also leads deterioration of high-speed property in forming images, which is originally an advantage of the high-speed machine. Although it is conceivable to enlarge a tank for storing the fixer fluid so as to eliminate necessity of the frequent replenishment of the fixer fluid, this leads to an increase in size of the image forming apparatus itself and is thus not preferable. Further, in the image forming apparatus of JP-A 2004-109747, the evaporation of the excess liquid is promoted by the heating section, with the result that a problem originally posed in the heat fixing method such that the warm-up time is necessary, has not been solved. If the image forming operation is performed in a state where a temperature of the heating section has yet been reached the predetermined temperature, the fixer fluid is pressed at a nip portion (contact portion) between the image carrier and the coating roller so that meniscus is formed at an entrance of the nip portion where the fixer fluid therefore stagnates, and the excess fixer fluid is attached to the coating roller again and made to be pushed back, in a consequence whereof there is a stream of the fixer fluid generated at the entrance of the nip portion. In addition, a mutually-binding force of toner particles constituting the toner image is weak and therefore, a part of the toner may be swept away. This may cause troubles such as irregularities of the toner image and thus irregularities of the image and fixing failure.